Conventional electric braking systems for aircraft are designed on the basis of architectures that are said to be “simple” or on architectures that are to be said “dissimilar”.
A “simple” architecture, corresponding to a portion of a braking system, is shown in FIG. 1. The portion of the braking system comprises a braking computer 1 and four electromechanical actuators 2, each comprising an electric motor. The electromechanical actuators 2 are designed to produce a pressing force in order to brake wheels of an aircraft.
The braking computer 1 comprises a braking control module 3, four motor control modules 4, and four inverters 5. The braking control module 3 executes software that performs a slow servo-control loop. Each motor control module 4 executes software that performs a fast servo-control loop. The braking control module 3 transmits a control setpoint to each motor control module 4. Each motor control module 4 controls the motor of one of the electromechanical actuators 2 via one of the inverters 5. This simple architecture is referred to herein as “centralized”, and would be said to be “distributed” only if each inverter 5 were remote, and positioned in the proximity of, or on, the electromechanical actuator 2 for which it participates in providing control.
A “dissimilar” architecture, corresponding to a portion of a braking system, is shown in FIG. 2. The braking computer 10 has two braking control modules 11, four motor control modules 12, and four inverters 13. The two braking control modules 11 are of designs that are mutually different in terms of hardware and/or software. Each braking control module 11 transmits a control setpoint to two motor control modules 12 in order to control the motors of two electromechanical actuators 14. This dissimilar architecture is referred to herein as “centralized”, and would be said to be “distributed” only if each inverter 13 were remote, and positioned in the proximity of, or on, the electromechanical actuator 14 for which it participates in providing control.
With a “simple” architecture, a common mode failure can lead to total loss of braking. With a “dissimilar” architecture, a common mode failure can lead to loss of no more than 50% of the braking (in the event of a failure in one of the braking control modules).
Nevertheless, it should be observed in order to improve the availability of commercial aircraft, that it is often required for braking performance to be guaranteed when one of the electromechanical actuators has failed (simple failure) and is no longer capable of producing a braking force. In such a situation, a common mode failure can lead to the loss of 75% of the braking with an architecture that is dissimilar: for a brake having four electromechanical actuators, only one electromechanical actuator remains controllable. With an architecture that is simple, such an event can lead to total loss of braking.